I'd call it focus stress. Unless context demands otherwise, primary phrasal stress tends to occur on the primary stressed syllable of the final word. Focus = primary phrasal stress occurring somewhere other than canonical position

In the example you give, I assume you've used allcaps to indicate phrasal stress occurring earlier than the final word (which ofc happens if discourse context motivates it)

But what semantic element is being focused? Stress shifting isn't the confusing thing here, that's just how it happens to surface in English. Focus makes sense, but presuming it is a focus mechanism... is it just propositional focus?

agreed, it feels like the same as fronting focus but just by making it pronounced more stressed instead of moving its position. same purpose and reception, different mechanism